For starters, brain cancer is so rare that some study groups included only a few dozen people, making it difficult to arrive at solid conclusions. And none of the studies included detailed data about frequency of exposure. A "regular user" in Interphone studies might talk on the phone just once a week, but could get the same weight as real estate agents glued to their Motorolas.

Several studies focused on which side of the head people held their phones. But quirky results made it clear that some people with cancer had skewed the data with faulty memory subconsciously aligning their phones near where they knew the tumor had occurred.

A huge Danish study in 2006 was widely trumpeted as putting the cell phone debate to rest. Instead of relying on small samples, the Danes found phone company records of 420,000 citizens who started using cell phones between 1982 and 1995. They cross-checked those names against the national cancer registry through 2002 and found no rise in tumors associated with phone use. The study included 58,000 people with at least 10 years of exposure.

But the study had flaws. Cancer risk for 10 years or more of phone use appeared to drop by one-third, an unlikely event. And the study mislabeled about 200,000 long-term users because their phones were owned by businesses that had doled them out to employees. Unable to identify who actually used each phone, the Danes simply eliminated those subscribers as long-term users.

That meant that 200,000 longtime users were classified as nonusers. If cell phones do cause cancer, that artificially raised the disease rate of "nonusers" and dampened the appearance of any cell phone-cancer link.

REASSURING RATES

One fact should reassure cell phone users: Brain cancer does not appear to be rising, not in the United States and not in Scandinavia, the wireless generation's Garden of Eden.

For 2006, the National Cancer Institute counted 6.1 brain cancer cases for every 100,000 Americans, the lowest rate in 25 years. Those numbers, the latest available, are now years old. But by 2006, about 40 million Americans had used cell phones for at least 10 years. If cell phones were indeed risky, cancer rates probably should have nudged up by now, said senior NCI investigator Peter Inskip.

"In the past, you could have said you are looking too soon, it takes a long time for tumors to appear," Inskip said. "But it's getting increasingly difficult to assert that."

David Carpenter, professor of environmental health sciences at Albany University, says there is "clear evidence" linking brain cancer and cell phone use. He speculated that declining exposure to toxic substances might be counter-balancing an increased risk from cell phones hence no rise in overall brain cancer.

It probably would not relate to declining cigarette use, Carpenter said. Smoking and brain cancer have no apparent link. But it might relate to toxic pesticides and industrial chemicals, he said. Some known to cause brain cancer were phased out over the last few decades.

Vanderbilt University epidemiologist John Boice said "there's not a glimmer of evidence" that brain cancer is on the rise.

High-frequency radiation, as from X-rays, does cause cancer because it is "ionizing," Boice said. Electromagnetic energy breaks down DNA bonds.

But "non-ionizing," low-frequency radiation has no cancer-causing mechanism, he said.

Consider radar, a low-frequency radiation that emits more energy than cell phones. Navy sailors from the Korean War were exposed to so much radar they could feel the heat, Boice says. Yet a study of 10,000 sailors showed no cancer increase.

Ditto microwave ovens. They create enough power and frequency to heat food but do not cause cancer, he says.

Still, studies suggesting a possible phone-cancer link are leading some scientists to maintain a middle-of-the road approach.

Meanwhile, five European countries have kicked off a study to end all studies. It will follow 250,000 subjects for 20 to 30 years to see who gets cancer. Records from cell phone providers will pinpoint exposure, down to the last minute.

In 30 years, teenagers probably will have shifted to the next new thing but at least we should have answers about cell phones.